Method and apparatus for printing a carrier material upon employment of a structure ice layer

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation Application of Ser. No. 09/355,432, filed Sep. 21, 1999, now U.S. Pat. No. 6,295,928.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method for producing a print image on a carrier material, whereby ink-attracting and ink-repelling areas are produced on a surface of a print medium according to the structure of the print image to be printed, whereby the ink-repellant areas are provided with a layer of an ink-repellant medium, ink is applied onto the surface, this adhering to the ink-attracting areas and not being picked up by the ink-repellant areas, and whereby the ink distributed on the surface is printed onto the carrier material.

The invention is also directed to an apparatus for producing a print image on a carrier material.

2. Description of the Related Art

Given a known offset printing process which works without water, the areas not to be printed are fat-repellant, they do not accept any ink. The areas to be printed, by contrast, are fat-attracting and can accept fat-containing ink. The ink-attracting and ink-repellant areas are distributed on a printing plate such that they reproduce the print image to be printed. The printing plate can be employed for a plurality of transfer printing events. A new printing plate with ink-attracting and ink-repellant areas must be produced for each print image.

Given the known direct imaging method of Heidelberger Druckmaschinen, a print master is produced in the printing system on a silicone-coated film by partially burning the silicone layer off. The silicone-free locations form the color-attracting areas and can pick color up during the printing process.

In another offset process working with water, hydrophobic and hydrophilic areas corresponding to the structure of the print image to be printed are produced on the print medium. Before applying ink to the print carrier, a thin moisture film is first applied onto the print carrier by employing application rollers or, respectively, sprayer devices, this wetting the hydrophilic area of the print carrier. With the assistance of an inking roller, ink is subsequently applied onto the surface of the print carrier; this, however, moistens only the areas not covered with the moisture film. After the inking of the print carrier, the ink print image is finally transferred onto the carrier material.

A method developed by Oce Printing Systems GmbH is also known wherein hydrophobic and hydrophilic areas are formed on the surface of the print carrier. The hydrophilic areas are moistened, so that no ink adheres to them. The surface of the print carrier is charged with water steam for moistening. The charging with water steam can also ensue such that hydrophilic areas arise corresponding to the structures of the print image to be printed. The ink is only picked up by areas that have not been provided with a moisture film. The aforementioned methods have the problem that the ink-water equilibrium must be very narrowly toleranced in order to achieve a high printing quality.

British patent document GB-A-1208731 discloses a method or, respectively, an apparatus for producing a print image on a carrier material. A substance in its solid phase is applied on a surface of a carrier material. This substance is heat sensitive and can be structured according to predetermined picture elements under the influence of heat, whereby this solid substance is removed. The uncovered surface of the print carrier can be brought into a hydrophilic condition. When inking with ink particles containing water, these adhere to the hydrophilic areas, whereas the hydrophobic areas of the substance in its solid phase repel these ink particles.

U.S. Pat. No. 3,741,118 discloses and method and an apparatus for printing an image, whereby a technique is utilized that approximately corresponds to a standard lithography technique. Upon application of electronic scanning technology, ink is selectively applied on a plate or an existing layer is selectively removed. The ink on the plate is then transferred onto paper. Subsequently, the plate is cleaned and can be prepared anew for the acceptance of ink.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and an apparatus for producing a print image on a carrier material that produces print images with high resolution and is largely compatible with previous printing processes or, respectively, printing devices.

This object is achieved by a method for producing a print image on a carrier material, including the steps of: producing ink-attracting and ink-repellant areas on a surface of a print carrier in conformity with a structure of the print image to be printed, providing the ink-repellant areas with a layer of an ink-repellant medium, supplying ink onto the surface, the ink adhering to the ink-attracting areas and being not picked up by the ink-repellant areas, printing the ink distributed on the surface onto the carrier material, using a substance in its solid phase as an ink-repellant medium in the ink-repellant areas, cooling the surface of the print carrier to produce the solid phase of the substance on the surface of the print carrier.

The employment of a solid substance as an ink-repellant medium has the advantage that a sharp boundary arises between ink-attracting and ink-repellant areas, as a result whereof the resolution of the print image is enhanced. Given employment of a substance in its solid phase, further, this does not run dry and no water streaks arise as is possible given traditional printing processes. The procedure known from offset printing for inking the print carrier and for transfer printing onto a carrier material can be retained.

An ice layer is preferably employed as an ink-repellant medium, this being deposited by condensation of water vapor in the environment of the print medium by spraying a thin water film or by application of a water film with rollers and subsequent formation of ice on the surface thereof. This ice layer has a defined form and a defined volume and offers relatively great resistance to a shape or volume change under the influence of external forces since the water molecules in the solid aggregate state are firmly bonded to one another at specific locations by electromagnetic interactions. The ink-repellant areas can thus be produced with a fine structure that leads to a print image having a high resolution. The ice layer becomes extremely uniform and thin as a result of adding an agent for reducing the surface tension of the water, preferably tensides or alcohol. The additives are located directly in the water and/or are applied on the print carrier by spraying or, respectively, application with a roller. Solid parting agents such as waxes, fats, resins or fatty acid amides can be employed as a further ink-repellant medium, these being applied onto the print carrier in the liquid condition by spraying or application with one or more rollers. The medium will convert into its solid phase on the printing plate which is cooled to below the solidification temperature of the respective substance.

In a preferred exemplary embodiment of the invention, the print-active surface of the print carrier is initially completely provided with an ice layer or with a parting agent layer composed of wax, fat, resin or fatty acid amides. In a following structuring process, ink-attracting areas that are free of said solid layer, for example of the ice layer or of the parting agent layer, are produced. Ink-attracting areas corresponding to the structure of the print image to be printed can be produced in this way.

In this exemplary embodiment, the surface of the print carrier need not be pre-treated according to the structure of the print image to be printed, for example by etching. On the contrary, the print-active surface is uniform and smooth in the initial condition. The structuring process merely comprises the production of areas which are free of solid bodies or, respectively, free of ice in conformity with the structure of the print image to be printed. In accord therewith, a plurality of print images can be produced on the surface of the print carrier, whereby the initial condition of the surface of the print carrier is to be produced for each print image. In this way, different print images can be produced without replacing the print carrier and can be inked and transfer-printed once or repeatedly. When a new print image is to be applied on the print carrier, then the print carrier is to be cleaned of the areas provided with the solid state layer or, respectively, ice layer as well as of ink residues, the surface is to be provided again with a solid state layer or, respectively, ice layer, and a new structuring process ensues.

The gradient energy of a laser beam or of an LED can be employed for selectively producing areas which are free of solid bodies or, respectively, free of ice on the surface of the print carrier. Another possibility is comprised in selectively producing the areas free of solid bodies by employing heating elements.

According to a further aspect of the invention, a means for implementing the disclosed method is recited.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained below with reference to the drawings.

FIG. 1 is a side view showing the schematic structure of an apparatus for offset printing, whereby an ice layer is produced on the plate cylinder; and

FIG. 2 is a side view showing an apparatus for printing, whereby areas with an ice layer are selectively produced on the print carrier.

FIG. 3 is a schematic representation of a spraying apparatus for applying water or parting agent; and

FIG. 4 is a schematic representation of a liquid applying roller for applying water or parting agent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows the structure of an apparatus for offset printing. It contains an inking unit <b>10</b> with three rollers <b>12</b>, <b>14</b> and <b>16</b> with which ink from an ink reservoir <b>18</b> is transferred onto the surface of a print carrier fashioned as a plate cylinder <b>20</b>. The inked surface of the plate cylinder <b>20</b> transfers ink onto a rubber coated cylinder <b>22</b> from this, the ink proceeds onto a paper web <b>24</b> that is pressed against the rubber blanket cylinder <b>22</b> by a counter-pressure cylinder <b>26</b>. The arrows entered in FIG. 1 indicate the respective conveying direction.

The plate cylinder <b>20</b> contains pipes for a coolant system <b>28</b> through which coolant is pumped. A cooling system <b>34</b> that offers coolant having the required temperature is connected to the coolant system <b>28</b> via hoses <b>30</b> and <b>32</b>. A pump P is inserted into the delivery line <b>32</b>. During operation, an ice layer condenses onto the hydrophilic areas of the surface of the plate cylinder <b>20</b>. This ice layer acts in an ink-repellant fashion, so that ink consequently does not precipitate on the ice layer. Ink is transferred from the drum <b>16</b> to the rubber blanket cylinder <b>22</b> on hydrophobic areas of the surface of the plate cylinder <b>20</b>. The hydrophilic and hydrophobic areas on the surface of the plate cylinder are applied in advance according to chemical-physical processes. An offset plate serving as print carrier is usually secured on the generated surface of the plate cylinder <b>20</b>. This offset plate is to be replaced for changing the print image.

FIG. 2 schematically shows a printing means, whereby different print images can be produced on the same surface of the print carrier. The print carrier is a continuous belt <b>40</b> here that is conducted around a deflection roller <b>42</b>, a transfer printing roller <b>44</b> and a cleaning roller <b>47</b>. The surface of the continuous belt <b>40</b> is cooled with a cooling device <b>46</b> to a temperature below the solidification point of water. In a case of a normal environment with average atmospheric humidity, the temperature of the surface of the continuous belt <b>40</b> lies below 0° C. The water vapor contained in the ambient air precipitates on the continuous belt <b>40</b> as ice layer as a result of condensation. Due to the optional application of a tenside with the roller, a uniformly thin ice layer is assured. The tenside application roller can, for example, be provided close to the transfer printing roller <b>44</b> or at the deflection roller <b>42</b> in an arrangement similar to that for the elements <b>12</b>, <b>14</b> and <b>18</b>. Another possibility is comprised in applying a thin water film having a thickness in the μm range. An ice layer then arises by cooling. A spraying process as shown in FIG. 3 can be utilized for applying the water film or the application ensues with the assistance of rollers as shown in FIG. <b>4</b>. The print-active surface of the continuous belt is thus completely provided with an ice layer. Subsequently, the ice layer is selectively removed by applying energy, for example by illumination with a laser beam <b>48</b>, as indicated in FIG. <b>2</b>. Alternatively to the ice layer, a parting agent layer of wax, fat, resin or fatty acid amide can also be employed, this being applied onto the print carrier in the liquid condition by being sprayed as shown in FIG. 3 or by being applied with one or more rollers as shown in FIG. <b>4</b>. The medium will convert into its solid phase on the printing plate cooled below the solidification temperature of the respective substance.

The illumination preferably ensues raster-like line-by-line, whereby the water of the ice layer converts into the vapor state. Other methods for producing ice-free areas employ, for example, the radiation of a laser diode or of an LED. Given an arrangement of an LED array in line form, an energy application can ensue simultaneously over the entire width of the continuous belt <b>40</b>, so that ice-free picture elements can be produced at high speed. It is also proposed that ice-free areas be produced upon employment of heating elements that are preferably arranged in a line.

The inking of the surface of the continuous belt <b>40</b> ensues with the assistance of the rollers <b>12</b> and <b>14</b> that transfer ink from the ink reservoir <b>18</b>. The ink agglomerates to areas without an ice layer. As mentioned, the areas carrying an ice layer are ink-repellant and do not accept any ink.

The transfer printing roller <b>44</b> transfers the ink distributed on the continuous belt <b>40</b> onto a carrier material <b>24</b> supplied from the right in FIG. <b>2</b>. The counter-pressure roller <b>26</b> presses the carrier material <b>24</b>, generally paper, against the transfer printing roller <b>44</b>.

Two operating modes are possible: in a first operating mode, the print image located on the continuous belt <b>40</b> is repeatedly inked and transfer-printed. For preserving the structured ice layer on the continuous belt <b>40</b>, further cooling devices <b>50</b> and <b>52</b> are provided that keep the ice layer below its solidification temperature.

In a second operating mode, a new print image is applied onto the continuous belt <b>40</b>. The previous structured ice layer is to be removed before this, as are the ink residues, and a defined initial condition is to be produced for the surface of the continuous belt <b>40</b>. To this end, a cleaning means <b>54</b> is activated at the cleaning roller <b>47</b>. It contains a wiper lip <b>56</b> and a brush <b>58</b> that are brought into contact with the surface of the continuous belt <b>40</b> and remove the structured ice layer. For activation and deactivation of the cleaning station <b>54</b>, this can be moved in the direction of the arrow <b>60</b>, such as by a motor. The additional cooling devices <b>50</b> and <b>52</b> are shut off in the second operating mode.

The cooling devices <b>46</b>, <b>50</b>, <b>52</b> can be constructed in the fashion of the cooling device in FIG. <b>1</b>. Another possibility is comprised in the employment of an electro-thermal cooling principle, for example by employing Peltier elements. It should also be mentioned that the surface of the continuous belt <b>40</b> is composed of metals, for example of stainless steel, nickel, copper, chromium, or of plastics such as, for example, polyamide, PE, polytetrafluoroethylene, or as composed of metallized plastics that bond the ink well at the ice-free locations and thus promotes achieving a high printing quality.

Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.